Sulfide ore beneficiation



United States Patent 3,252,662 SULFIDE ORE BENEFICIATHON John W. Lyons, Webster Groves, and Robert P. Langguth, @verland, Mo, assignors to Monsanto (Iompany, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Aug. 20, 1962, Ser. No. 218,109

. 18 Claims. (Cl. 241-16) This invention relates to beneficiating ores by flotation and more particularly the invention relates to improved flotation methods in which the state of flocculation of an ore being processed is controlled to effect a more efiicient separation of mineral values.

The use of deflocculating and flocculating agents in ore beneficiation procedures has previously been suggested but prior to this invention no procedure has been suggested for efiiciently making use of such agents and no flotation procedure employing a combination of such agents has achieved any degree of commercial success.

It has now been found that the addition to an ore during early stages of processing of a defiocculating agent results in the formation of an aqueous slurry or pulp from which mineral values can be more readily extracted by modified flotation techniques and that advantage can be taken of this action of a deflocculating agent if, subsequent to rough classification, the further step of adding a flocculating agent is performed to assist in water recovery. V

A process in accordance with this invention has numerous advantages, one of which is that it results in a substantial increase in grinding efficiency. A first step in ore processing normally comprises wet grinding the ore, and deflocculation of the pulp in a wet grinding unit permits the use of higher pulp densities for a given fluidity. This results in more ore particles per unit volume and hence more contacts between particles and grinding media per unit time which, therefore, in effect increases the capacity of the grinding apparatus. Also, since there is less resistance to particle movement in a deflocculated pulp as compared to an untreated pulp of the same fluidity, the fine ore particles are more readily removed by the mills classifying action so that, relatively speaking, more grinding energy is used in disintegrating large ore particles and less is wasted in overgrinding the fines. The over-all result is that less energy is used per unit of solids ground to a given fineness, or a finer grind per unit of energy is obtained. The improvement with respect to overgrinding fines is in itself a major advance since overgrinding of fines can result in increased slime formation.

Another important advantage of a process in accordance with this invention is that one normally obtains an improved efiiciency in classification of the ore solids. Substantially all wet ore beneficiation procedures employ some means of classifying particles according to sizeweight relationships and, since deflocculation lessens interparticle attractions and thereby removes a major barrier to free movement of the particles, classification in moderate force fields is greatly improved. Thus, the overflow from units such as spiral or rake classifiers and wet cyclones contains a smaller percentage of oversize particles when the feed to these units is deflocculated.

A process in accordance with this invention also has the advantage that less difficulty is encountered from slimes. Slimes reduce the efficiency of froth flotation procedures by coating the surfaces of the mineral hearing particles so that they become in effect barren particles with no exposed sites for the adsorption of collector molecules. The collector is chemically tailored for adsorption only upon the exposed mineral-bearing surfaces. Slimes may be spontaneously formed during ore processing by coarse grinding naturally occuring clays, or slimes ice may be formed by fine grinding of barren minerals such as shales, feldspars, quartz and the like. In accordance with this invention, fine grinding of barren minerals to produce slimes is held to a minimum as mentioned above. In addition, the deflocculating agent in most instances appears to adsorb on the surfaces of the ore particles and by establishing repulsive forces between slime particles and the desired mineral-bearing particles prevents formation of slime coatings that would interfere with the recovery action of the collector. The slimes remain thus suspended until flocculation is effected at a subsequent step in the process.

The most important advantage of a process in accordance with this invention is that it permits a substantial improvement in the extent to which a selected mineral value can be recovered from an ore containing the same by froth flotation techniques. In most instances the improvement in recovery that can be effected in accordance with this invention is about 5% and in some instances the improvement may be as much as 10* to 20%. Considering the extent to which froth flotation procedures are employed, the conservation of scarce natural resources which can be effected by the present invention is indeed substantial.

The present invention is of interest with respect to any ore which is processed by froth flotation but the invention is particularly useful with sulfide ores and will be described primarily with respect to such ores. Industrial flotation has been more widely employed in the treatment of sulfide ores of the base metals than for any other application and it is an advantage of the present invention that it is particularly suited for use in the processing of such ores. Specific examples of metals which are recovered from sulfide ores include copper, lead, and zinc, and Well known examples of ores from which such metals are recovered include the chalcocite and'chalcopyrite ores of Arizona.

While any type of deflocculating agent can suitably be employed in a proces in accordance with this invention, the linear condensed phosphates, sometimes referred to as chain phosphates, are preferred because of their inexpensiveness and availability. Examples of this class of deflocculants include the pyrophosphates, tripolyphosphates and Water-soluble glassy phosphates of any available chain length. The particular salt employed is not of great importance except that heavy metal and alkaline earth metal salts, as is well known, do not function efficiently as deflocculating agents and for this reason an alkali metal salt is preferably employed. In lieu of a salt, the corresponding free acid can be employed in instances where it is available since, for reasons which will subsequently be explained, the pulp in most instances is basic and the use of a free acid under these conditions is equivalent to the use of a salt. The sodium salts are r usually preferred for reasons of economy. Specific examples of suitable materials include sodium acid pyrophosphate, tetrapotassium pyrophosphate, sodium tripolyphosphate, tetrasodium pyrophosphate, the material available commercially under the name of sodium hexametaphosphate which is an amorphous glass of a composition normally equivallent to Na -R 0 and the water soluble glassy polyphosphate available from Monsanto Chemical Company under the trade name SQ Phosphate.

It is an advantage of the invention that only minor changes in the manipulative procedure and in the apparatus conventionally employed need be made in order to practice an improved process in accordance with this invention. In fact, other than the controlled addition of flocculating and defiocculating agents, the only major change necessitated by the new process is that the use of large quantities of compounds which release alkaline earth metal ions must be avoided in some instances during the grinding, classification and rougher flotation operations. This is because most deflocculants are not effective in the presence of unsequestered alkaline earth metal ions, and for the full advantages of the new process to be realized the deflocculating agent must be used under such conditions that it is fully effective. A sequestering agent or an excess of the defiocculant when it, as is frequently the case; acts as an alkaline earth metal ion sequestrant can be added to eliminate the undesirable effect of calcium or other alkaline earth metal ions, but this adds to the expense of the process and where possible it is generally preferable to have the pulp substantially free of unsequestered alkaline earth metal ions at the time the deilocculant is added. Lime is employed in many flotation operations for pH adjustment and as a pyrite depressant and in view of the above it will be apparent that other bases and/or pyrite depressants should be employed in a process in accordance with this invention.

For pH adjustment one can employ sodium hydroxide,

potassium hydroxide, or any other base which does not provide ions that interfere with the action of the defiocculating agent. In instances where the use of a pyrite depressant is desirable or necessary and the use of lime would undesirably interfere with the action of the defiocculating agent, one can employ sodium cyanide or other conventional pyrite depressants which do not provide alkaline earth metal ions.

The defiocculating agent is added in accordance with this invention prior to or during the grinding operation conventionally utilized to provide a particle size suitable for flotation. This is because it has been found, as previously mentioned, that the deflocculating agent material ly improves the efficiency of the grinding operation and this is particularly true when, as is usually the case, a ball mill or similar apparatus is employed for grinding.

While any degree of deflocculation of the pulp during the grinding and usually during the flotation operations is beneficial and some improvement can be obtained by adding even very small amounts of a deflocculating agent, in most instances it is advantageous to add an amount of the defiocculant which will result in a near maximum reduction in the viscosity of the pulp. The amount of defiocculant required to effect this result will depend upon a number of variables including the specific nature of the pulp and the effectiveness of the defiocculant under the conditions of operation, but an optimum amount can readily be determined in each instance by routine test. The use of large excesses of defiocculant is not normally advantageous because, as will subsequently be explained, the action of the defiocculant must be neutralized prior to the thickening operation which constitutes a subsequent step in the process. These considerations usually dictate the use of from about 0.1 to 5 lbs. of deflocculating agent per ton of ore and preferably from about 0.5 to 2.0 lbs. of defiocculant per ton of ore.

There are several ways that one can take advantage of the increase in grinding efficiency which results from the addition of a deflocculating agent. One convenient way comprises increasing the ore solids concentration of the material fed to the grinding mill. One can then maintain the volume output of the mill at a conventional level to produce a pulp in which the solids have approximately the same mean particle size as in previous practice. The concentration of ore solids during grinding has in the past ranged from about 50 to 75 solids but in accordance with this invention the solids concentration in some instances suitably can be as high as 85% solids, the preferred range being from 60 to 80% solids.

The procedure immediately following the initial grinding operation can be conventional and, for example, a preliminary separation can be made by means of a rake classifier or the like or by means of a preliminary flotation cell so that the oversized ore particles can be subjected to regrinding and only the proper size material forwarded to the rougher flotation unit. The flotation apparatus can be of conventional design and can comprise agitation cells, subaeration cells, cascade cells, pneumatic cells or various combinations of such cells. Likewise the density (percent solids), pH and temperature of the pulp can be the same as in conventional practice. For example, most flotation operations with sulfide ores are conducted under basic conditions and if such conditions are necessary for efiicient operation of the process they can advantageously be employed in accordance with the present invention. It should be mentioned, however, that since lime is employed as a pyrite depressant in many flotation operations and since other pyrite depressants are frequently preferable in accordance with the present invention, it is often advantageous from the point of view of reagent costs to operate at a lower pH, for example, from about pH 7.5 to 10, than is conventional when using lime. If desired, however, the pulp can have a pH of 12 or higher. As for the other two process variables mentioned above, a pulp density of from about 20 to 50% solids by weight is most frequently employed in accordance with conventional flotation practice and is quite satisfactory in accordance with the present invention although pulp densities as high as ore solids can be employed in some instances; and the usual temperatures of from 10 to 30 C. are satisfactory in accordance with this invention although a heated pulp may be employed Where conventionally advantageous, for example, in molybdenum-copper differential separations.

There are conventionally employed in froth flotation operations such reagents as collectors, suppressants, frothing agents and the like, and with the exception of alkaline earth ion liberating materials, all such conventional reagents are suitable for use in a process according to this invention. Illustrative examples of suitable anionic collectors include alkali metal alkyl xanthates, such as potassium amylxanthate, sodium ethylxanthate, and potassium n-butylxanthate; alkyl and aryldithiophosphoric acids and their alkali metal or ammonium salts such as sodium diisopropyl dithiophosphate and ammonium di-sec-butyl dithiophosphate (these compounds are commercially available under the trademark Aerofloat); and fatty acids such as oleic acid and lauric acid. Cationic collectors are not compatible with the condensed phosphate deflocculating agents and where the action of such a defiocculating agent is desired during the flotation operation, the use of such collectors is not normally desirable. However, if one uses a deflocculating agent and other reagents with which cationic collectors are compatible, such collectors can be employed in accordance with this invention for the flotation of ores with which they are conventionally used. From about 0.005 to 0.3 lb. of collector per ton of ore normally produces satisfactory results. Typical frothing agents which are conventionally employed and which can he employed in accordance with this invention include pine oil, aliphatic alcohols such as methylamyl alcohol, cresylic acid, and alkylene oxide phenol condensates. Such frothers can be employed in amounts ranging from about 0.05 to 0.2 lb. per ton of ore. Other assistants such as foam stabilizers, depressants and activators are also frequently employed in conventional flotation practice and can be similarly employed in the processes of this invention where desired.

Following rougher flotation the mineral concentrate can be processed in a conventional manner. The concentrate will contain some active defiocculant in instances where a flocculating agent is not added prior to rougher flotation and this can be allowed to remain in an active state to assist in subsequent flotation operations or it can be inactivated immediately subsequent to rougher flotation by the addition of a flocculating agent such as lime. The latter procedure is sometimes advantageous where pyrite is \a serious problem since lime is an excellent pyrite depressant.

The machine discharge product or tailings from the rougher flotation unit is passed to a thickener to effect recovery of at least a part of the water. Water recovery and reuse is normally necessary to avoid a severe disposal problem and because in most areas sufficient water is not readily available to operate profitably without at least a partial recovery of the water from tailings. Water is generally recovered by means of various types of intermittent or continuous thickeners and any type of thickening apparatus conventionally employed can be used in accordance with this invention.

It has been found that in order to effect satisfactory recovery of water from the tailings when a deflocculating agent is employed to facilitate flotation it is necessary to add a flocculant to the tailings prior to or during the thickening operation. In other words, the deflocculant normally acts .to permit the very fine particles in the tailings to remain in suspension for exceedingly long periods of time, and in order to effect gravity separation of the suspended solids it is necessary that the pulp be flocculated. To effect flocculation one can employ any of the well known flocculating agents as illustrated by potassium alum, magnesium sulphate and the synthetic polymeric flocculants sold under the trademarks Separan and Aerofloc. The preferred flocculating agent, however, is a combination of lime and synthetic polymeric flocculant. Any excess flocculating agent employed to effect thickening and water recovery will adversely affect the grinding and flotation operations when the water is reemployed to form a new pulp unless the flocculating agent is made ineffective. and for this reason it is usually advantageous to employ only so much of the flocculating agent as is required to effect satisfactory thickening of the pulp. The amount of the flocculating agent required is dependent upon its effectiveness and upon the amount of deflocculating agent added to the pulp during or previous to flotation, but generally an amount of flocculant equal to from /2 to 5 times the weight of the deflocculant employed in .the process normally can be used satisfactorily. In instances where a mixture of inorganic and organic polymer flocoulants is employed, as is normally preferred, the weight ratio of inorganic to organic flocculants can advantageously range from about 5 to 1 to 100 to 1. For example, from about 0.5 to 5 lbs. of an inorganic flocculant, such as lime, usually can be advantageously employed with from about 0.005 to 0.5 lb. of an organic polymer flocoulant, such as hydrolyzed polyacrylonitrile, per ton of ore solids.

An exception to the rule that it is not advantageous to employ an excess of the flocculating agent sometimes exists in the case of lime. When lime is employed as the only deflocculant or as the major constitutent of a deflocculant mixture, any reasonable excess over that required to effect satisfactory water recovery can be made readily ineffective as a flocculating agent by the addition of an alkali metal carbonate, such as sodium carbonate, to precipitate calcium carbonate. The alkali metal hydroxide thereby formed serves to make a new pulp basic when the recovered water is employed in its formation and, as previously mentioned, a basic pulp is normally desired in flotation and in particular in sulfide ore flotation. 2

The invention will be more particularly illustrated by the following specific example in which all parts are by weight:

Example Arizona chalcopyrite ore curshed to a maximum size of about /2 inch is fed to a ball mill of standard design with suflicient water and recycle pulp from a classifier to produce a pulp in the mill of 73 solids and is simultaneously mixed with 1.0 lb. of sodium tripolyphosphate per ton of ore solids, sufficient NaOH to produce a pH in the mill of about 11 (usually about 1 to 2 lbs. of NaOH per ton of ore solids), and 0.02 lb. of sodium isopropyl xanthate per ton of ore solids. The ore is then ground in an otherwise conventional manner. In one test of this procedure it was found that grinding efficiency was equivalent to that obtained under strictly comparable conditions except that the slurry of ore being ground contained 68% ore solids and except that in place of the sodium tripolyphosphate and sodium hydroxide the slurry contained 4.0 lbs. of lime per ton of ore. It will be seen, therefore, that on the basis of mill output per unit of time the grinding efliciency of the mill was increased by approximately 14%.

The ball mill output is fed to a submerged spiral classifier (a rake classifier is also satisfactory) to effect a preliminary gravity separation of the over-sized material so that it can be recycled for further grinding. The pulp density in the sump of the submerged spiral classifier is maintained at about 25-30% by weight solids. The efficiency of the classifier on the deflocculated pulp is noticeably superior to that found in flocculated pulps.

The overflow from the spiral classifier is mixed with 0.1 lb. of sodium cyanide and 0.1 lb. of n-octyl alcohol per ton of ore solids, the purpose of the cyanide being to serve as a pyrite depressant and the purpose of the alcohol being to serve as a frothing agent. The resulting mixture, which normally has a pH of about 10, is then fed to a row of square type roughing flotation cells where it is subjected to froth flotation using otherwise conventional techniques. In small scale tests of this procedure it has been found that the percent of the total copper found in the concentrate in most instances is approximately 5% higher than when a similarly processed flocculated pulp is subjected to flotation in the identical manner. Further, the improvement in copper recovery is retained through subsequent conventional flotation cleaning operations.

The tailings or machine discharge pulp from the rougher flotation cells is first mixed with 2.0 lbs. per ton of lime and then with 0.02 lb. per ton of Separan AP-30 (a synthetic polymeric flocculant sold by Dow Chemical Company) and is passed to a conventional tailings thickener. The substantially floc-free water recovered from the thickener is mixed with 0.5 lb. per ton of sodium carbonate and is used in forming a slurry of ore solids in the ball mill. The water subsequent to the sodium carbonate addition is basic so that once the recycle arrangement is placed in operation the amount of sodium hydroxide required to adjust the pH of the aqueous slurry in the ball mill to the desired level of about pH 10 is very small and, indeed, by the use of a controlled excess of lime for flocculation of the tailings the recycle water can be made by the addition of sodium carbonate to have such a pH that no sodium hydroxide at all need be added.

The procedure when using other deflocculating agents, flotation agents and flocculating agents is generally the same as set forth in the above example.

Having thus described our invention and one preferred specific embodiment thereof, what we desire to secure and claim by Letters Patent is:

1. An improved method for recovering values from a sulfide ore, which method comprises subjecting said ore while in an aqueous slurry, containing a deflocculating agent and an amount sufficient to provide a pH of at least 7.5 of a base compatible with said defiocculating agent, to a grinding operation to thereby form a deflocculated pulp of said ore, thereafter, without performing any intermediate operation on said pulp to effect removal of slirnes therefrom, subjecting said pulp containing said defiocculating agent to froth flotation to obtain a mineral concentrate and a machine discharge pulp, thereafter adding a flocculating agent to said machine discharge pulp to effect flocculation of suspended material therein, and separating liquid for reuse in the production of an aqueous ore pulp from thus flocculated material.

2. A method according to claim 1 wherein said froth flotation is a rougher stage of flotation.

3. A method according to claim 1 wherein said defiocculating agent is a linear condensed alkali metal phosphate.

4. A method according to claim 1 wherein said defiocculating agent is a linear condensed alkali metal phosphate and said flocoulating agent comprises lime.

5. A method according to claim 4 wherein said flocculating agent is a mixture of lime and an organic polymer fiocculant.

6. A method according to claim 4 wherein said alakli metal phosphate is sodium tripolyphosphate.

7. A method according to claim 4 wherein said alkali metal phosphate is sodium hexametaphosphate.

8. A method according to claim 4 wherein said ore is a copper sulfide ore.

9. A method for recovering mineral values from a metallic sulfide ore which comprises grinding said ore while in an aqueous slurry containing an amount of a linear condensed alkali metal phosphate suflicient to effect at least partial deflocculation of the ore solids in the resulting pulp and additionally containing an amount suflicient to provide a pH of at least 7.5 of a base compatible with said alkali metal phosphate, thereafter, without performing any intermediate operation on said pulp to effect removal of slimes therefrom, subjecting the thus ground ore to froth flotation in the presence of said condensed alakli metal phosphate and an anionic collecting agent to obtain a mineral concentrate and a machine discharge product, adding an amount of a flocculating agent to said discharge product to effect flocculation of the suspended solids in said discharge product, separating liquid from the thus fiocculated solids, inactivating excess flocculating agent in the thus separated liquid, and thereafter using said liquid in the production of an aqueous ore pulp.

10. A method for recovering copper values from a copper sulfide ore which comprises grinding said ore to produce an aqueous pulp thereof, said pulp containing an amount of a linear condensed alkali metal phosphate suflicient to effect at least partial deflocculation of the ore solids therein and said pulp being substantially free of unsequestered alkaline earth metal ions, adjusting the pH of the pulp to from about 8 to 12, subjecting the basic pulp to froth flotation in the presence of an anionic collecting agent to obtain an ore concentrate and a machine discharge product, adding an amount of a flocculating agent to said discharge product, said flocculating agent comprising lime as a major constituent and said amount being in excess of that required to effect flocculation of the suspended material in said discharge product, separating a substantially floc-free aqueous liquid from the thus fiocculated discharge product, adding to the thus separated liquid an amount, at least suflicient to react with the lime present in said separated liquid, of an alkali metal carbonate, separating the resulting precipitate of calcium carbonate from said liquid, and using the resulting, substantially calcium-free, basic aqueous liquid for the production of ore pulp.

11. A method according to claim 10 wherein said alkali metal carbonate is sodium carbonate and said flocoulating agent is a mixture of lime and an organic polymer flocculant.

12. A method according to claim 11 wherein said linear condensed phosphate is sodium tripolyphosphate.

13. A method according to claim 11 wherein said linear condensed phosphate is sodium hexametaphosphate.

14. A method according to claim 1'1 wherein said linear condensed phosphate is tetrasodium pyrophosphate.

15. A method according to claim 11 wherein suflicient excess lime is employed to result in said aqueous liquid having a pH of from about 9 to 11 following the addition of said sodium carbonate.

16. A method for recovering metal values from a sulfide ore which comprises grinding an aqueous slurry of said ore containing from to by weight ore solids to produce an aqueous pulp thereof, said slurry additionally containing from 0.1 to 5 lbs. of a linear condensed alkali metal phosphate per ton of said ore solids to effect at least partial deflocculation of the ore solids in said slurry, said slurry being substantially free of unsequestered alkaline earth metal ions and having a pH of from about 8 to 12, diluting the resulting ore pulp such that it contains from 20 to 50% solids, subjecting the diluted pulp to froth flotation in the presence of an anionic sulfide collecting agent to obtain an ore concentrate and a machine discharge product, adding to said discharge product from about 0.5 to 5 lbs. of flocculating agent per ton of solids in said discharge product, separating a substantially floc-free aqueous liquid from the thus flocculated discharge product, inactivating excess flocculating agent in the thus separated liquid, and thereafter using said liquid in the production of an aqueous ore pulp.

17. A method according to claim .16 wherein said flocculating agent comprises lime as a major constituent and excess flocculating agent is inactivated by the addition of sodium carbonate.

18. A method according to claim 17 wherein said condensed alkali metal phosphate is sodium tripolyphosphate.

References Cited by the Examiner UNITED STATES PATENTS 843,426 2/ 1907 Acheson 209-5 1,454,838 5/ 1923 Borcherdt 209-5 1,585,756 5/ 1926 Borcherdt 209-5 1,604,125 10/1926 Kern 210-52 X 1,737,717 12/1929 Hardy 209-5 1,802,989 4/1931 Thomas 209-163 2,012,830 8/1935 Ralston 209-107 2,014,407 9/1935 Weed 209- 2,186,095 1/1940 Booge 241-16 2,352,324 6/1944 H-ubler 241-24 2,383,106 8/1945 Booth 209-166 X 2,428,228 9/1947 Keck 209-5 2,525,146 10/ 1950 McMurray 209-166 X 2,868,618 1/1959 Oberg 209-5 X 2,909,508 10/1959 Jones 210-52 X 3,032,197 5/ 1962 Northcott 20-9-166 3,061,097 10/ 1962 Dering 209-5 HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner. 

1. AN IMPROVED METHOD FOR RECOVERING VALUES FROM A SULFIDE ORE, WHICH METHOD COMPRISES SUBEJECTING SAID ORE WHILE IN AN AQUEOUS SLURRY, CONTAINING A DEFLOCCULATING AGENT AND AN AMOUNT SUFFICIENT TO PROVID A PH OF AT LEAST 7.5 OF A BASE COMPATIBLE WITH SAID DEFLOCCULATING AGENT, TO A GRINDING OPERATION TO THEREBY FORM A DEFLOCCULATED PULP OF SAID ORE, THEREAFTER, WITHOUT PERFORMING ANY INTERMEDIATE OPERATION ON SAID PULP TO EFFECT REMOVAL OF SLIMES THEREFROM, SUBJECTING SAID PULP CONTAINING SAID DEFLOCCULATING AGENT TO FROTH FLOTATION TO OBTAIN A MINERAL CONCENTRATE AND A MACHINE DISCHARGE PULP, THEREAFTER ADDING A FLOCCULATING AGENT TO SAID MACHINE DISCHARGE PULP TO EFFECT FLOCCULATION OF SUSPENDED MATERIAL THEREIN, AND SEPARATING LIQUID FOR REUSE IN THE PRODUCTION OF AN AQUEOUS ORE PULP FROM THUS FLOCCULATED MATERIAL. 